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Getting the Jump on ’03 Weed Control

Monday, September 2, 2002
filed under: Weeds

Getting the Jump on ’03 Weed Control

Have you decided where your 2003 sunflower acreage will be located? What problem weeds are in those fields? Are they perennials whose control would be enhanced by a fall herbicide treatment? Will your schedule be any less hectic next spring than it is this fall?

Northern Plains sunflower producers may want to ask themselves such questions as they ponder a jump-start on '03 weed control during next month or two.

"A fall application provides a good foundation weed control program," affirms Richard Zollinger, extension weed specialist with North Dakota State University. That's particularly true, he says, if you're regularly battling tough perennials like Canada thistle or field bindweed. Late-summer/early fall liquid herbicide applications are ideal for deep-rooted perennials like Canada thistle, Zollinger suggests, because the still-warm temperatures allow effective translocation of systemics down into the roots.

Canada thistle has a very extensive root system, 90-plus percent of which lies below cultivation depth. So conventional — as well as no-till — producers can really benefit from an early fall herbicide treatment to manage this weed.

If moisture is adequate, many growers utilize a pre- or post-harvest glyphosate treatment (alone or with 2,4-D) on this year's wheat ground to attack Canada thistle and other perennials. Curtail, dicamba, Stinger and Tordon are other options. Growers must, however, be aware of carryover restrictions for the upcoming crop before making fall applications of such herbicides. (Only corn, wheat, soybeans and sorghum — not sunflower — are recommended for planting the spring following a fall application of Banvel, for instance.)

While at it, don't forget about those nearby fence lines, pastures and ditches, Zollinger adds. They can be a fertile source of weed seeds which will later end up in your fields. A single Canada thistle plant can produce more than 5,000 seeds — seeds which can be transported by the wind for up to 200 feet from the mother plant.

Another facet of the fall herbicide application story for next year's sunflower ground is, of course, a late-fall granular application of trifluralin (e.g., Treflan) or Sonalan. Those treatments are very economical, Zollinger points out — and with granules, "you're not hauling water, so you can cover a lot of acres in a short period of time."

Brett Oemichen, market development manager for DowAgrosciences in the Northern and High Plains, says the actual percentage of growers who fall-apply granules on next year's sunflower ground varies from year to year. While part of the reason is simple economics (i.e., wanting to delay chemical costs until the following spring), a bigger reason, he believes, is farm program-driven decisions over which fields will contain sunflower the following season.

"Some growers [conduct] fall application just because it helps spread out their workload," Oemichen observes. "Also, a granular herbicide application works extremely well with fall application of anhydrous ammonia. The two are easy to combine." Granulars are particularly suited for controlling annual weeds like kochia, pigweed and the grasses.

The current labels for trifluralin and Sonalan granules recommend at least one mechanical incorporation. In recent years, however, some no-till and minimum-till sunflower producers have opted for surface applications, counting on winter snow melt and early spring rains to incorporate the chemical. While that approach is legal — and has worked well in a number of instances — it presently is not on the product label, so the grower has no recourse should weed control prove unsatisfactory.

If one is going to surface-apply granules, these circumstances will increase the odds of success:

• Later is better. If you can accurately predict winter's first snowfall, apply the granules the day before. If you can't, right around Halloween is a good target date in the Northern Plains.

• If you're a no-till producer, employ the practice on a field that has been in no-till for at least two or three years. By then, most weed seeds will be germinating from the surface layer of soil, not lower.

• Standing stubble helps protect the granules from degradation. The stubble also enhances snow catch, which later will translate into better incorporation and chemical activation.

• A pass with an implement like the Phoenix rotary harrow will allow the herbicide to come into contact with some soil while causing only minimal residue disturbance.

As another option, a few sunflower producers are looking at a fall application of FMC Corporation's new pre-emergent herbicide, Spartan.

Sam Tutt, Minnesota-based technical services manager for FMC, says fall applications of Spartan have been tested extensively in Montana on fallow ground. The treatments have been quite successful on weeds like kochia and Russian thistle, he reports, providing control for up to nine or 10 months when applied at 2.5 to 3.0 oz per acre.

As yet, Spartan does not have a federal label for sunflower, operating instead under a series of Section 18 labels in several sunflower-producing states.

Tutt emphasizes that the current Section 18s for Spartan on sunflower do not list fall application as an approved practice. FMC does intend to include a fall application option on Spartan's eventual federal label. But until then — or until a given state includes it on a Section 18 — it is not an approved use for this product and cannot be recommended.

Tutt does encourage sunflower producers to contact their state department of agriculture if this is an option they'd like to see for Spartan use in their state, as these departments are the originators of Section 18 applications.

So a fall application on next year's sunflower ground is not for you — whether by choice or by default? If that's the case, NDSU's Rich Zollinger has two final suggestions: (1) "Don't plant sunflower in trashy fields." (2) "Get your weeds under control in the other crops." Those steps, coupled with the effective use of in-season herbicides and/or cultivation, still should give you the upper hand in your battle with the weeds. — Don Lilleboe

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